Many industries, including but not limited to oil well drilling, machining, mining, quarrying, and transportation, use mechanisms that need to work under high pressure and high temperature conditions. Furthermore, parts of the mechanisms often rub against each other or external surfaces and, therefore, a low friction, abrasion resistant surface in these parts is desired.
One solution, for example, is a bearing surface comprised of Polycrystalline Diamond Compact (PDC), a synthetic diamond that performs under harsh conditions. PDC is diamond grit that has been fused together under high-pressure, high-temperature conditions in the presence of a catalytic metal. The extreme hardness, wear resistance, and thermal conductivity of diamond make it an ideal material for bearings. Individual diamond crystals cleave quite easily when struck parallel to certain planes (the process used to facet diamond gemstones takes advantage of these relatively weak planes). Diamond sintering overcomes the problem of weak planes in diamond gemstones by bonding a mass of small diamond particles onto a larger, coherent structure. Sintered diamond provides greater toughness and durability than single crystals because the individual crystals in a sintered body are randomly oriented. This prevents cracks from propagating along the weak planes where traditional diamond crystals cleave most easily. Sintered diamonds also provide more uniform wear than a single crystal, while maintaining similar thermal conductivity and hardness properties. All of these factors combine to make sintered diamond the ideal material for many bearing applications.
However, overtime, PDC bearings do wear out and can become damaged from intensive use. The PDC bearings are usually embedded into the device by welding and, therefore, in order to replace the PDC bearings, the parts must be removed from operation and transported to a specialized facility that is able to remove the worn out PDC bearings and replace them with new bearings. The process is both costly and time consuming. Furthermore, the repeated heating and cooling needed to replace the bearings causes excessive stress on the devices. Additionally, the welded or brazed bearing pads currently used during refurbishment cannot maintain precision tolerances, especially after multiple replacements. Therefore, it is desirable to have a replaceable low-friction, abrasion resistant bearing surface capable of being replace quickly on-site.
In some applications, the need for a larger diameter bearing surface makes the use of use of PDC bearings prohibitive. One such application is as a stand-off to hold the cutters of a reamer off the casing string while drilling out a shoe. In this application, the life of the bearing surface needs to be greater than the time during which the reamer is rotated inside the casing. However, it is not practical to transport the tool to a central shop for replacement of the bearing surface after each run. The use of cheaper materials, such as tool steel, Teflon, nylon, etc., which are capable of surviving a single pass in the well bore become practical in this application when a field replaceable retention system is employed.